The thesis is devoted to the development of novel broadband light-trapping structures based on regular arrays of nanostructures and microstructures often referred in the modern literature as metamaterials. Our suggested light-trapping structures offer the gain in the optical efficiency of thin-film solar cells of several types without damaging their operational characteristics. These types of photovoltaic devices include thin-film solar cells based on amorphous silicon, organic and perovskite materials. In the first part, we present a metal light-trapping structure based on arrays of nanoantennas and report its theoretical and experimental studies. We reveal unusual eigenmodes in arrays of metal elements with domino-like proportions and show that in the optical range of frequencies they may composite a broad frequency band comparable with the operation band of a realistic solar cell. We experimentally confirm the existence of these modes and theoretically prove their light-trapping functionality. We design the optimal array of metal nanoantennas supporting these modes and theoretically demonstrate the enhancement of the useful absorption for a realistic organic solar cell. Finally, we present experimental results demonstrating an increase of the overall power conversion efficiency granted by our light-trapping structure compared to the reference solar cell with a conventional design. In the second part, we discuss novel all-dielectric light-trapping structures and report the results of full-wave numerical simulations. For amorphous silicon-based thin-film solar cell, we study the suppression of both reflection and transmission granted by the following systems: a flat antireflection coating, an array of densely packed polystyrene nanospheres, and arrays of nanovoids (cylindrical and tapered shape, both in the PMMA layer). We optimize the geometrical parameters to obtain the highest absorption in the photovoltaic layer and reveal light-trapping properties of these structures. Finally, we suggest and study a universal light-trapping structure for solar cells of 3rd generation. The structure consists of an array of dielectric truncated cones serving as the tapered optical waveguides for the incident light and optically connected to the thin-film solar cell through the holes in the metal film (e.g., Au). We theoretically show the advantages of our solution with respect to known analogs: it grants a gain in the PV absorption both in case of the organic thin-film SC (more significant) and perovskite thin-film SC (less significant but still noticeable). The existing techniques allow us to fabricate such a structure rather simply and quickly without involving expensive materials or processes. We believe that the presented results are helpful for the further development of thin-film solar cells of these three types.
|Tila||Julkaistu - 2018|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|